This invention relates in general to video signal apparatus and in particular, to a color video printer for producing a color photographic copy from a color video signal.
It is often desirable to make a color photographic print of an image displayed on a color video monitor. One technique is to use a still camera to take a photograph directly of the screen of the video monitor. However, this technique can produce a poor quality copy due to the difficulty in synchronizing the shutter speed of the still camera with the frame rate of the video signal. Moreover, it is difficult to position the still camera relative to the monitor screen in order to make the photographic image coincide with the monitor image. Another technique which has been proposed (see, e.g., U.S. Pat. Nos. 4,438,453 and 4,473,849) is to divide the color video signal into red, blue and green component video signals and to sequentially display images of the respective component signals on a monochrome monitor. The screen of the monitor is photographed through stationary color filters corresponding to the color component signals applied to the monitor. The exposure time in this technique is long since color film is exposed to several frames of each color component signal. This technique is time consuming and is not readily applicable to the copying of a moving video scene.
Several sophisticated techniques have been disclosed (see, e.g., U.S. Pat. Nos. 4,373,156; 4,339,769; and 4,468,693) in which a frame store is utilized to capture a frame of a color video signal. A color print is made by sequentially exposing color photographic material to timed exposures of sequential color images of the captured frame. These systems are disadvantageous in their size, structural and circuit complexity and high cost. Other proposed printing techniques have also proved unsatisfactory. Thus, techniques requiring chemical processing of exposed photographic material (e.g. U.S. Pat. No. 3,006,260) or thermal transfer of print material from transfer paper to copy paper (e.g., U.S. Pat. No. 4,496,955), necessitate replenishment of toxic chemicals or handling of messy transfer materials. Furthermore, techniques which require special purpose printing tubes (e.g., U.S. Pat. Nos. 4,231,061 and 2,995,619) are costly and complex.
A relevant technique is disclosed in U.S. Pat. No. 2,878,309 relating to the field sequential color broadcast system which was briefly authorized as the United States Color Broadcast Standard during the early 1950's. In the disclosed system, a color television signal comprising a sequence of red (R), green (G), and blue (B) field video signals is applied to a monochrome television tube which is reviewed through a rotating RGB filter wheel as a color image. A frame of color motion picture film is exposed to a sequence of six fields to produce a full resolution motion picture image of the video signal. It would be difficult, however, to use such a system in making a color copy of a present day standard composite color video signal since no means is disclosed for selecting a single component color video signal from three concurrent color component video signals. Moreover, the motion picture film had to be subsequently processed after all of the frames have been exposed so that a frame was not available for immediate viewing.
Thus, there exists a need for a simple, economical and easy to use color video printer for producing a color photographic copy of a color video signal.